Separation process having an alcohol sidestream

ABSTRACT

Recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid. The crude ethanol product is fed to a distillation column to yield an ethanol sidestream.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to a low energy process for recoveringethanol.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, unreacted acetic acid remains in thecrude ethanol product, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol product;separating at least a portion of the crude ethanol product in adistillation column into a distillate comprising ethyl acetate, asidestream comprising ethanol, and a residue comprising acetic acid andwater; and recovering ethanol from the sidestream.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid from anacetic acid feed stream in a reactor to form a crude ethanol product;separating at least a portion of the crude ethanol product in adistillation column into a distillate comprising ethyl acetate, asidestream comprising ethanol and water, and a residue comprising aceticacid; and reducing the water content of the sidestream to yield anethanol product stream having a reduced water content.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol productcomprising ethanol, acetic acid, water, and ethyl acetate; separating atleast a portion of the crude ethanol product in a distillation columninto a distillate comprising ethyl acetate, a sidestream comprisingethanol, and a residue comprising acetic acid; and recovering ethanolfrom the sidestream.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system thatyields an ethanol sidestream in accordance with one embodiment of thepresent invention.

FIG. 2 is a schematic diagram of an ethanol production system having awater separator for dewatering the ethanol sidestream in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, unreacted acetic acid, and otherimpurities. To improve operating efficiencies, the processes of thepresent invention involve separating the crude ethanol product into adistillate stream comprising the ethyl acetate or other light-weighthydrocarbons, a sidestream comprising the ethanol product, and a residuestream comprising water and unreacted acetic acid. Preferably, theseparation is performed in a single column Advantageously, thisseparation approach results in reducing capital requirements relative toother separation approaches for recovering ethanol from the crudeethanol product. In addition, overall energy requirements, resultingfrom fewer columns, pumps and/or heat exchangers, may also be reduced byusing a primary distillation column as described herein. In oneembodiment, the process may use a single distillation column having anethanol sidestream.

In one embodiment, at least 90% of the ethanol in the crude ethanolproduct is withdrawn as the ethanol sidestream, e.g., at least 94% ofthe ethanol or at least 96% of the ethanol. In terms of compositionalranges, the ethanol sidestream may comprise ethanol in an amount from 50to 90 wt. %, e.g., from 55 to 75 wt. % or from 60 to 70 wt. %. Theethanol sidestream may also comprise less than 0.1 wt. % acetic acid,e.g., less than 0.01 wt. % acetic acid. In a preferred embodiment, theethanol sidestream may be substantially free of acetic acid andcomprises less than 500 ppm acetic acid. In addition, the ethanolsidestream may also comprise less than 9 wt. % ethyl acetate, e.g., lessthan 3 wt. % or less than 2.5 wt. %.

In some embodiments, the ethanol sidestream may also comprise water,e.g., from 10 to 45 wt. % water or from 20 to 40 wt. % water. Dependingon the desired use for the ethanol product, it may be desirable toremove water from the ethanol sidestream Accordingly, the separationprocesses of the present invention may include a water separation unit,e.g., a distillation column, one or more membranes, one or moreadsorption units, or a combination thereof. Suitable adsorption unitsinclude pressure swing adsorption (PSA) units and thermal swingadsorption (TSA) units. The adsorption units may comprises molecularsieves, such as aluminosilicate compounds.

Recovering ethanol from a sidestream of a column may allow a substantialportion of the water fed to the column to be withdrawn as in theresidue. In one embodiment, at least 44% of the water in the crudeethanol product is withdrawn in the residue, e.g., at least 52% of thewater or at least 62% of the water. The acetic acid from the crudeethanol product may also be withdrawn in the residue. The overallcomposition of the residue may vary depending, for example, on aceticacid conversion, as discussed below, as well as the composition of thecrude ethanol product and the separation conditions in the columnDepending largely on the composition, the residue may be: (i) entirelyor partially recycled to the hydrogenation reactor, (ii) separated intoacid and water streams, (iii) treated with a solvent in a weak acidrecovery process, (iv) reacted with an alcohol to consume unreactedacetic acid, or (v) sent to a waste water treatment facility fordisposal. If the residue is separated into acid and water streams, theseparated acid preferably is recycled to the hydrogenation reactor.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orstream reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally, in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen, which may be used in connection with this inventionas noted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation step optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB, VIB,VIIB, VIII transition metals, a lanthanide metal, an actinide metal or ametal selected from any of Groups IIIA, IVA, VA, and VIA. Preferredmetal combinations for some exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, andruthenium/iron. Exemplary catalysts are further described in U.S. Pat.No. 7,608,744 and U.S. Pub. No. 2010/0029995, the entireties of whichare incorporated herein by reference. In another embodiment, thecatalyst comprises a Co/Mo/S catalyst of the type described in U.S. Pub.No. 2009/0069609, the entirety of which is incorporated herein byreference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium More preferably, the third metal is selected from cobalt,palladium, and ruthenium When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain NorPro. The Saint-GobainNorPro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseunreacted acetic acid, ethanol and water. As used herein, the term“crude ethanol product” refers to any composition comprising from 5 to70 wt. % ethanol and from 5 to 40 wt. % water. Exemplary compositionalranges for the crude ethanol product are provided in Table 1. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70  15to 50 25 to 50 Acetic Acid 0 to 90 0 to 50 15 to 70 20 to 70 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product may comprise acetic acid inan amount of less than 20 wt. %, e.g., of less than 15 wt. %, less than10 wt. % or less than 5 wt. %. In embodiments having lower amounts ofacetic acid, the conversion of acetic acid is preferably greater than75%, e.g., greater than 85% or greater than 90%. In addition, theselectivity to ethanol may also be preferably high, and is greater than75%, e.g., greater than 85% or greater than 90%.

Ethanol Recovery Systems

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1 and 2. The hydrogenation system100 provides a suitable hydrogenation reactor and a process forseparating ethanol from the crude reaction mixture. System 100 comprisesreaction zone 101, which comprises reactor 103, and separation zone 102,which comprises separator 106, and primary distillation column 107. Inthe embodiment shown in FIG. 2, separation zone 102 further comprises awater separator 108.

As shown in FIG. 1, hydrogen and acetic acid are fed to a vaporizer 109via lines 104 and 105, respectively, to create a vapor feed stream inline 110 that is directed to reactor 103. In one embodiment, lines 104and 105 may be combined and jointly fed to the vaporizer 109. Thetemperature of the vapor feed stream in line 109 is preferably from 100°C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C.Any feed that is not vaporized is removed from vaporizer 109 and may berecycled or discarded. In addition, although line 110 is shown as beingdirected to the top of reactor 103, line 110 may be directed to theside, upper portion, or bottom of reactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid, to form ethanol. In oneembodiment, one or more guard beds (not shown) may be used upstream ofthe reactor, optionally upstream of vaporizer 109, to protect thecatalyst from poisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product stream is withdrawn, preferablycontinuously, from reactor 103 via line 111.

The crude ethanol product stream in line 111 may be condensed and fed toa separator 106, which, in turn, provides a vapor stream 112 and aliquid stream 113. Suitable separators 106 include one or more flashersor knockout pots. The separator 106 may operate at a temperature of from20° C. to 250° C., e.g., from 30° C. to 250° C. or from 60° C. to 200°C. The pressure of separator 106 may be from 50 kPa to 2000 kPa, e.g.,from 75 kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally, thecrude ethanol product in line 111 may pass through one or moremembranes, not shown, to separate hydrogen and/or other non-condensablegases therefrom.

The vapor stream 112 exiting separator 106 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 104 andco-fed to vaporizer 109. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 104.

The liquid stream 113 from separator 106 is withdrawn and pumped to theside of primary distillation column 107. In one embodiment, the contentsof liquid stream 113 are substantially similar to the crude ethanolproduct obtained from the reactor, except that the composition has beendepleted of hydrogen, carbon dioxide, methane and/or ethane, whichpreferably are removed by separator 106. Accordingly, liquid stream 113may also be referred to as a crude ethanol product. Exemplary componentsof liquid stream 113 are provided in Table 2. Liquid stream 113 maycontain other components not specifically listed in Table 2.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 113) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 70 10 to 60  15 to 50 Acetic Acid <905 to 80 15 to 70 Water 5 to 40 5 to 30 10 to 30 Ethyl Acetate <30 0.001to 20     1 to 12 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <50.001 to 2    0.005 to 1    Acetone <5 0.0005 to 0.05   0.001 to 0.03 Other Esters <5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 OtherAlcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout presentspecification are preferably not present and if present may be presentin trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the liquid stream 113may comprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. It should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol product in line 111 or in liquid stream 113may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol.

Liquid stream 113 is introduced in the middle part of primarydistillation column 107, e.g., middle half or lower third. In column107, water and unreacted acetic acid, along with any other heavycomponents, if present, are removed from liquid stream 113 and arewithdrawn, preferably continuously, as residue in line 114. Column 107also forms an overhead distillate, which is withdrawn in line 115, andwhich may be condensed and refluxed, for example, at a ratio of from10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

Primary distillation column 107 also removes ethanol in a sidestream116. Preferably, sidestream 116 comprises less than 500 wppm aceticacid. Sidestream 116 may be withdrawn above the feed point of the liquidstream 113. In one embodiment, column 107 has a hat tray and sidestream116 is withdrawn from the hat tray or at a location above the hat tray.Depending on the location of where sidestream 116 is withdrawn fromcolumn 107, sidestream 116 may be a vapor or a liquid. Optionally, aslipstream 120 from sidestream may be returned to column 107, such asless than 5% of the sidestream 116.

Although one sidestream 116 is shown in FIG. 1, it should be understoodthat in some embodiments, there may be more than one ethanol sidestream,for example, if the simultaneous production of multiple grades ofethanol is desired.

When column 107 is operated under 170 kPa pressure, the temperature ofthe residue exiting in line 114 preferably is from 115° C. to 125° C.The temperature of the distillate exiting in line 115 preferably is from70° C. to 90° C. The temperature of the sidestream 116 preferably isfrom 82° C. to 100° C. at 100 kPa, e.g., from 96° C. to 100° C. at 170kPa or from 82° C. to 86° C. at 100 kPa. In some embodiments, thepressure of column 107 may range from 0.1 kPa to 510 kPa, e.g., from 1kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary components of thedistillate, sidestream and residue compositions for column 107 areprovided in Table 3 below. The distillate, sidestream and residuestreams may contain other components not specifically listed in Table 3.

TABLE 3 PRIMARY DISTILLATION COLUMN Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Ethanol 45 to 90 50 to 85 55 to 80 Water  2 to 20  4to 15  6 to 12 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate<60 5.0 to 40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4  Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025Sidestream Ethanol 50 to 90 55 to 75 60 to 70 Water 10 to 45 20 to 40 20to 30 Ethyl Acetate 0.01 to 9   0.1 to 3   0.01 to 2.5  Residue AceticAcid <60 0.1 to 40   2 to 30 Water 50 to 98 60 to 98 70 to 98 Ethanol <2<0.9 <0.07

Some species, such as acetals, may decompose in column 107 such thatvery low amounts, or even no detectable amounts, of acetals remain inthe distillate or residue. In addition, an equilibrium reaction betweenacetic acid and ethanol or between ethyl acetate and water may occur inthe crude ethanol product after it exits reactor 103. Depending on theconcentration of acetic acid in the crude ethanol product, thisequilibrium may be driven toward formation of ethyl acetate. Thisequilibrium may be regulated using the residence time and/or temperatureof the crude ethanol product.

Although distillate in line 115 also comprises ethanol, the relativeweight ratio of ethanol in the distillate and sidestream is greater than1:10, greater than 1:15 or greater than 1:20. In one embodiment, primarycolumn 107 has a mass flow ratio for the distillate to sidestream toresidue of about 1:25:7.

The finished (or final) ethanol product preferably is derived fromethanol sidestream 116. Although it is preferred to withdraw most of thewater in the residue of column 107, in some embodiments, the water maybe withdrawn with the ethanol in sidestream 116. Further separation ofthe water and ethanol using one or more water separators 108 may bebeneficial to control the amount of water in the finished ethanolproduct. Depending on the composition of ethanol sidestream 116, one ormore water separators 108 may be used to recover a dry, preferablyanhydrous, ethanol product from ethanol sidestream 116 having a reducedwater content relative to ethanol sidestream 116. In FIG. 2, a waterseparator 108 is used to remove residual water from ethanol sidestream116. Particularly, preferred techniques include the use of adistillation column, one or more membranes, one or more adsorption unitsor a combination thereof. Suitable adsorption units include pressureswing adsorption (PSA) unit and thermal swing adsorption (TSA) unit. Adistillation column, used in combination with a PSA or membrane, may bepreferred when the water concentration in the sidestream is greater than10 wt. %.

As shown in FIG. 2, water separator 108 is a pressure swing adsorption(PSA) unit. The PSA unit optionally is operated at a temperature of from30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressure of from0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit maycomprise two or three beds. Water separator 108 optionally removes atleast 90% of the water from ethanol sidestream 116, and more preferablyfrom 95% to 99% of the water from ethanol sidestream 116 to form waterstream 117. All or a portion of water stream 117 may be returned tocolumn 107 and ultimately recovered in the residue in line 114 of column107, or purged via line 117. The remaining portion of sidestream 116exits water separator 108 as a finished ethanol product 118.

Using one or more membranes as the water separator 108 may produce apermeate stream comprising water and a retentate stream comprisingethanol. In this aspect, the retentate stream preferably has a lowerwater concentration than ethanol sidestream 116.

Depending on the amount of water and acetic acid contained in theresidue of column 107, the residue in line 114 may be treated in one ormore of the following processes. The following are exemplary processesfor further treating first residue and it should be understood that anyof the following may be used regardless of acetic acid concentration.When the residue comprises a majority of acetic acid, e.g., greater than70 wt. %, the residue may be recycled to the reactor without anyseparation of the water. In one embodiment, the residue may be separatedinto an acetic acid stream and a water stream when the residue comprisesa majority of acetic acid, e.g., greater than 50 wt. %. Acetic acid mayalso be recovered in some embodiments from first residue having a loweracetic acid concentration. The residue may be separated into the aceticacid and water streams, for example, by a distillation column or one ormore membranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream preferably is returned to reactor 103. The resulting waterstream may be used as an extractive agent or to hydrolyze anester-containing stream in a hydrolysis unit.

In other embodiments, for example where the residue in line 114comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the residue to reactor 103, (ii)neutralizing the acetic acid, (iii) reacting the acetic acid with analcohol, or (iv) disposing of the residue in a waste water treatmentfacility.

It also may be possible to separate a residue comprising less than 50wt. % acetic acid using a weak acid recovery distillation column towhich a solvent (optionally acting as an azeotroping agent) may beadded. Exemplary solvents that may be suitable for this purpose includeethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 114 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts ofacetic acid, e.g., less than 5 wt. %, the residue may be sent to a wastewater treatment facility for disposal without further processing. Theorganic content, e.g., acetic acid content, of the residue beneficiallymay be suitable to feed microorganisms used in a waste water treatmentfacility.

The distillate in line 115 preferably comprises ethanol, ethyl acetate,and acetaldehyde and may refluxed as shown in FIG. 1, for example, at areflux ratio of from 1:10 to 10:1, e.g., from 1:5 to 5:1 or from 1:3 to3:1. In one aspect, not shown, the distillate or a portion thereof maybe returned to reactor 103. In some embodiments, it may be advantageousto return a portion of distillate to reactor 103. The ethyl acetateand/or acetaldehyde in the distillate may be further reacted inhydrogenation reactor 103 to produce additional ethanol.

Optionally, distillate in line 115 may be processed to produce asecondary ethanol product may separating the ethyl acetate and/oracetaldehyde. The secondary ethanol product may be suitable as ansolvent or as a mixed stream for an esters production facility.

In some embodiments, the distillate in line 115 may also comprise up to12 wt. % water. If all or a portion of the distillate is returned to thereactor, it may be necessary to remove water from line 115. The water inthe distillate in line 115 may be removed, for example, by an adsorptionunit, one or more membranes, extractive distillation, or a combinationthereof.

In another embodiment, not shown, the distillate in line 115 may be fedto acetaldehyde removal column to recover acetaldehyde that may berecycled to the reactor 103. In the acetaldehyde removal column, thedistillate is separated into a second distillate, which comprisesacetaldehyde and a second residue, which comprises ethyl acetate. Thedistillate preferably is refluxed at a reflux ratio of from 1:20 to20:1, e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and a portion of thesecond distillate is returned to reaction zone 101. For example, thesecond distillate in line 115 may be combined with acetic acid feed 105,added to vaporizer 109, or added directly to reactor 103. Without beingbound by theory, since acetaldehyde may be hydrogenated to form ethanol,the recycling of a stream that contains acetaldehyde to the reactionzone increases the yield of ethanol and decreases byproduct and wastegeneration. In another embodiment, the acetaldehyde may be collected andutilized, with or without further purification, to make useful productsincluding but not limited to n-butanol, 1,3-butanediol, and/orcrotonaldehyde and derivatives thereof.

The primary column 107 of the present invention, and any otherdistillation columns used with embodiments of the present invention, maybe any distillation column capable of performing the desired separationand/or purification step. Each column preferably comprises a tray columnhaving from 1 to 150 trays, e.g., from 10 to 100 trays, from 20 to 95trays or from 30 to 75 trays. The trays may be sieve trays, fixed valvetrays, movable valve trays, or any other suitable design known in theart. In other embodiments, a packed column may be used. For packedcolumns, structured packing or random packing may be employed. The traysor packing may be arranged in one continuous column or they may bearranged in two or more columns such that the vapor from the firstsection enters the second section while the liquid from the secondsection enters the first section.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

In one embodiment, the final ethanol product produced by the process ofthe present invention may be taken from ethanol sidestream 116. Theethanol product may be an industrial grade ethanol comprising from 75 to96 wt. % ethanol, e.g., from 80 to 96 wt. % or from 85 to 96 wt. %ethanol, based on the total weight of the ethanol product. Exemplaryfinished ethanol compositional ranges are provided below in Table 4.

TABLE 4 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

As discussed above in connection with FIG. 1, residual water may beremoved from ethanol sidestream 116 to form an anhydrous ethanol productstream, i.e., “finished anhydrous ethanol,” using one or more additionalseparation systems, such as, for example, distillation columns (e.g., afinishing column), membranes, adsorption units, or molecular sieves.Anhydrous ethanol may be suitable for fuel applications. In suchembodiments, the ethanol concentration of the finished ethanol productmay be greater than indicated in Table 4, and preferably is greater than97 wt. % ethanol, e.g., greater than 98 wt. % or greater than 99.5 wt.%. The finished ethanol product in this aspect preferably comprises lessthan 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entire contents and disclosures ofwhich are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite YinU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedherein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. It should be understood thatthis example is for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

EXAMPLE 1

The following examples were prepared with ASPEN Plus 7.1 simulationsoftware to test various feed composition and separation systems.

A mixture comprising 56 wt. % ethanol, 38 wt. % water, 2 wt. % ethylacetate, 2 wt. % acetaldehyde, 1 wt. % acetic acid, and 1 wt. % otherorganics is fed into a single distillation column with a side draw. Thecolumn has 49 theoretical stages. The feed is located at the 20th stagefrom the top and the side draw is located at the 10^(th) stage from thetop. The mass flow rate ratio of distillate, sidestream, and residue is3:76:21. The compositions of the distillate, sidestream, and residue areshown in Table 5.

TABLE 5 Distillate Side draw Residue (wt. %) (wt. %) (wt. %) Ethanol77.3%  70.5% <0.01% Water 11.5%  23.3%   95.5% Ethyl Acetate 4.4% 2.5%<0.01% Acetic Acid <0.01%    0.1%    4.5% Acetaldehyde 3.5% 1.8% <0.01%Other Organics 3.3% 1.8% <0.01%

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising the steps of:hydrogenating acetic acid from an acetic acid feed stream in a reactorto form a crude ethanol product; separating at least a portion of thecrude ethanol product in a distillation column into a distillatecomprising ethyl acetate, a sidestream comprising ethanol, and a residuecomprising acetic acid and water; and recovering ethanol from thesidestream.
 2. The process of claim 1, wherein at least 90% of theethanol in the crude ethanol product is removed in the sidestream. 3.The process of claim 1, wherein the sidestream comprises 50 to 90 wt. %ethanol, and 10 to 45 wt. % water.
 4. The process of claim 1, whereinthe sidestream comprises less than 500 ppm acetic acid.
 5. The processof claim 1, wherein the sidestream further comprises water and theprocess further comprises reducing the water content of the sidestreamto yield an ethanol product stream with reduced water content.
 6. Theprocess of claim 5, wherein the ethanol product stream comprises lessthan 3 wt. % water.
 7. The process of claim 5, wherein the reducing stepuses an adsorption unit.
 8. The process of claim 5, wherein the reducingstep comprises separating at least a portion of the sidestream with amembrane into a permeate stream comprising water and a retentate streamcomprising ethanol and having a lower water concentration than thesidestream.
 9. The process of claim 1, wherein the residue comprises 2to 30 wt. % acetic acid, 70 to 98 wt. % water, and less than 2 wt. %ethanol.
 10. The process of claim 1, further comprising recoveringacetic acid from the residue and returning at least a portion of therecovered acetic acid to the reactor.
 11. The process of claim 1,wherein the distillate further comprises ethanol.
 12. The process ofclaim 1, wherein a portion of the distillate is returned to the reactor.13. The process of claim 1, wherein the acetic acid is formed frommethanol and carbon monoxide, wherein each of the methanol, the carbonmonoxide, and hydrogen for the hydrogenating step is derived fromsyngas, and wherein the syngas is derived from a carbon source selectedfrom the group consisting of natural gas, oil, petroleum, coal, biomass,and combinations thereof.
 14. A process for producing ethanol,comprising the steps of: hydrogenating acetic acid from an acetic acidfeed stream in a reactor to form a crude ethanol product; separating atleast a portion of the crude ethanol product in a distillation columninto a distillate comprising ethyl acetate, a sidestream comprisingethanol and water, and a residue comprising acetic acid; and reducingthe water content of the sidestream to yield an ethanol product streamhaving a reduced water content.
 15. The process of claim 14, wherein theethanol product stream comprises less than 3 wt. % water.
 16. Theprocess of claim 14, wherein at least 90% of the ethanol in the crudeethanol product is removed in the sidestream.
 17. A process forproducing ethanol, comprising the steps of: providing a crude ethanolproduct comprising ethanol, acetic acid, water, and ethyl acetate;separating at least a portion of the crude ethanol product in adistillation column into a distillate comprising ethyl acetate, asidestream comprising ethanol, and a residue comprising acetic acid; andrecovering ethanol from the sidestream.
 18. The process of claim 17,wherein at least 90% of the ethanol in the crude ethanol product isremoved in the sidestream.